Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$92.38	10.850%	$102.4032	$102.40	$102.40	$102.40
Purchase #2	$153.51	10.597%	$169.7775	$169.78	$169.80	$169.80
Purchase #3	$175.93	4.852%	$184.4661	$184.47	$184.45	$184.50
Purchase #4	$41.54	3.111%	$42.8323	$42.83	$42.85	$42.80
Purchase #5	$25.90	13.674%	$29.4416	$29.44	$29.45	$29.40
Purchase #6	$99.35	4.826%	$104.1446	$104.14	$104.15	$104.10
Purchase #7	$35.54	3.483%	$36.7779	$36.78	$36.80	$36.80
7 purchase totals =	$624.15		$669.8432	$669.84	$669.90	$669.80